, Volume 187, Issue 2, pp 289-298

Elevated CO2 evokes quantitative and qualitative changes in carbon dynamics in a plant/soil system: mechanisms and implications

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Abstract

It is hypothesized that carbon storage in soil will increase under an elevated atmospheric CO2 concentration due to a combination of an increased net CO2 uptake, a shift in carbon allocation pattern in the plant/soil system and a decreased decomposition rate of plant residues. An overview of several studies, performed in our laboratory, on the effects of elevated CO2 on net carbon uptake, allocation to the soil and decomposition of roots is given to test this hypothesis. The studies included wheat, ryegrass and Douglas-fir and comprised both short-term and long-term studies.

Total dry weight of the plants increased up to 62%, but depended on nutrient availability. These results were supported by the data on net 14CO2 uptake. A shift in 14C-carbon distribution from shoots to roots was found in perennial species, although this depended on nutrient availability.

The decomposition experiments showed that roots cultivated at 700 μL L−1 CO2 were decomposed more slowly than those cultivated at 350 μL L−1 CO2. Even after two growing seasons differences up to 13% were observed, although this was found to be dependent on the nitrogen level at which the roots were grown.

Both an increased carbon allocation to the soil due to an increased carbon uptake, whether or not combined with a shift in distribution pattern, and a decreased decomposition of root residues will enhance the possibilities of carbon sequestration in soil, thus supporting our hypothesis. However, nutrient availability and the response of the soil microbial biomass (size and activity) play a major role in the processes involved and require attention to clarify plant/soil responses in the long term with regard to sustained stimulation of carbon input into soils and the decomposability of roots and rhizodeposition. Soil texture will also have a strong effect on decomposition rates as a result of differences in the protecting capacity for organic matter. More detailed information on these changes is needed for a proper use of models simulating soil carbon dynamics in the long term.